Until now, as a production method for a polyacetal copolymer, a cationic copolymerization with trioxane as a main monomer, and a cyclic ether and/or cyclic formal having at least one carbon-carbon bond as a comonomer has been known. As the cationic active catalyst used for these copolymerizations, a Lewis acid, in particular halides of boron, tin, titanium, phosphorous, arsenic, and antimony, for example boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorous pentachloride, phosphorous pentafluoride, arsenic pentafluoride, and antimony pentafluoride, and their complex compounds or salts; protonic acids for example perchloro acids; esters of protonic acids, in particular esters of perchloro acids and lower aliphatic alcohols, for example perchloro acid-tertiary butyl ester; anhydrides of protonic acids, especially mixed anhydrides of perchloro acids and lower aliphatic carboxylic acids, for example acetyl perchlorate, or trimethyloxonium hexafluorophosphate, triphenyl-methylhexafluoroacetate, acetyltetrafluoroborate, acetylhexafluorophosphate, and acetylhexafluoroarsenate, and the like have been proposed. Among these, boron trifluoride, or coordination compounds of boron trifluoride and organic compounds, for example ethers, are the most common as polymerization catalysts with trioxane as the main monomer, and are widely used industrially.
However, in generally used polymerization catalysts such as boron trifluoride compounds or the like, a relatively large amount of the catalyst (for example 40 ppm or more with respect to the total monomers) is necessary for polymerization. Therefore, problems may arise such as difficulty in carrying out sufficient catalyst deactivation treatment after polymerization, and even if deactivated, substances deriving from the catalyst may remain in the copolymer, and may promote decomposition of the copolymer, or the like. Further, it is usual that the deactivation process of the catalyst is carried out in a large amount of an aqueous solution comprising a basic compound such as triethylamine or the like, and after the catalyst deactivation complex operations become necessary, such as separating the processing liquid from the copolymer and drying, recovering the unreacted monomer dissolved in the processing liquid, and the like, which also include economical problems.
In order to eliminate such complications accompanying the deactivation process of the catalyst, a method of adding a tertiary phosphorous compound to the produced copolymer (for example, refer to Patent Document 1 and the like), and a method of adding a hindered amine compound (refer to Patent Document 2 and the like) have been proposed, but the desired effects have not been obtained.
In contrast to this, a production method for a polyacetal copolymer using a heteropoly acid as a catalyst has been proposed (for example, refer to Patent Document 3 and the like). Further, a production method for a polyacetal copolymer has been proposed where, after carrying out the preparation of a crude polyacetal copolymer by copolymerization with a heteropoly acid as a catalyst, a solid basic compound which is at least one selected from a triazine ring-containing compound having an amino group or a substituted amino group, and a polyamide, is added to the reaction products, and deactivation of the catalyst is carried out by a melt kneading process (for example, refer to Patent Document 4 and the like). According to these methods, because heteropoly acids have high activity it becomes possible to polymerize with an extremely small amount of catalyst, and it is possible to provide a high quality polyacetal copolymer. Further, because the deactivation of the catalyst is carried out by a melt kneading process substantially without using a solvent, complex processes such as those mentioned above are not required, which is also economically favorable.
Patent Document 1: Japanese Examined Patent Application Publication No. S55-42085
Patent Document 2: Japanese Unexamined Patent Application, Publication No. S62-257922
Patent Document 3: Japanese Unexamined Patent Application, Publication No. H01-170610
Patent Document 4: Japanese Unexamined Patent Application, Publication No. 2003-026746